Lubricating oil processing

ABSTRACT

Lubricating oils of high-viscosity index are produced in good yield by a sequence involving mild hydrogenation, solvent refining and dewaxing. The process is particularly effective for the treatment of lube oil fractions containing at least 1 percent Conradson Carbon Residue using N-methyl pyrrolidone as the solvent.

United States Patent Inventor Robert A. Woodle Nederland, Tex'.

Appl. No. 815,233

Filed Apr. 10, 1969 Patented Nov. 2, 1971 Assignee Texaco Inc.

New York, N.Y.

LUBRICATING 01L PROCESSING [56] References Cited I UNITED STATES PATENTS3,414,506 12/1968 Van Lookern 208/18 Compagne 3,472,757 10/1969 Morriset a1. 208/18 3,201,344 8/1965 Broughton 208/143 3,425,932 2/1969Surrena et al... 208/143 3,436,334 4/1969 Orkin et al 208/18 PrimaryExaminer1-1erbert Levine Attorneysl(. E. Kavanagh, Tl-Iomas H. Whaleyand Robert Knox, Jr.

ABSTRACT: Lubricating oils of high-viscosity index are produced in goodyield by a sequence involving mild hydrogenation, solvent refining anddewaxing. The process is particularly effective for the treatment oflube oil fractions containing at least 1 percent Conradson CarbonResidue using N-methyl pyrrolidone as the solvent.

LUBRICATING OIL PROCESSING This invention is concerned with thetreatment of lubricating oil stocks. More particularly, it is concernedwith a novel processing scheme whereby lubricating oil stocks areconverted in good yields into high quality lubricating oils.

Various procedures are available for the refining of lubricating oils.For example solvent refining is used to remove low Vl aromatic compoundsand reactive impurities by contacting the oil with a solvent whichpreferentially dissolves aromatic compounds. As a substitute for solventrefining, it has been proposed to subject the lubricating oil stock torelatively severe catalytic hydrotreating conditions for the saturationof aromatic compounds. This generally carried out at a pressure betweenabout 1,000 and 2,000 p.s.i.g. Another step in the refining of the lubeoil'stocks is solvent dewaxing for the removal of high-melting point waxand correspondingly a reduction in the pour point of the oil. This isaccomplished by adding a preferential solvent for the oil, chilling andfiltering. Clay contacting has been employed to remove color clay bodiesfrom the oil to produce an oil of improved color. Color improvement canalso be effected by mild hydrogenation, for example, at a relatively lowtemperature and pressure as distinguished from the hydrogen treatmentfor aromatic saturation to improve the viscosity index.

In conventional lube oil refining the solvent extraction step is carriedout first to recover about 45-75 percent of the charge as refined oiland to reject about 25-55 percent of the charge as dark colored viscousextract. Since the extract amounts to a relatively large percentage ofthe charge and is not suitable for upgrading by dewaxing and either claycontacting or mild hydrogenation to a satisfactory quality level for useas a lube oil, solvent extraction has, up to the present,- been the mostlogical and economical process to apply first.

The refiner then has the option of removing color bodies from the oil bymild hydrogenation or clay treating and then reducing the pour point ofthe oil by solvent dewaxing or by following the solvent refining withsolvent dewaxing and then with clay contacting or mild hydrogenation.The choice between these two sequences is usually made on the basis ofwhich one is the most practical for a given refinery. For example, if afinished refined wax is to be produced dewaxing may be chosen ahead ofmild hydrogenation to permit separate treatment of the wax. Differentconditions would then be used on the dewaxed oil than would be used ifthe hydrogenation were to precede the solvent dewaxing in which case waxwould be present in the charge to the hydrogenation reactor.

It is an object of the present invention to providea novel sequence forthe treatment of the lube oil stocks to increase the yield of highquality lubricating oils. Another object is to produce lubricating oilsof improved properties such as viscosity index and color. Another objectis to reduce the amount of solvent necessary for the solvent refining ofa particular lubricating oil. These and other objects will be obvious tothose skilled in the art from the following disclosure.

According to my process, a lubricating oil stock is first subjected tomild hydrogenation, the hydrogenation product is then solvent refinedand the solvent refined material is then dewaxed. l have found that bythe process of my invention yields of refined oil obtained in thesolvent refining step are in the range of about -20 percent higher byvolume basis charge to the extraction zone when refining to the samequality level than when no mild hydrogenation precedes the solventrefining. In addition, as compared to raw stocks the mildly hydrogenatedstocks have higher APl gravities, lower refractive indexes and higherviscosity indexes. My novel process also permits reduction in theseverity of the solvent extraction conditions whereby refining solventdosages can be reduced when charging the mildly hydrogenated stocks.This means that in existing units the capacity can be increased or, inunits to be built, smaller units can handle the desired throughput.

The process of my invention may be applied to any lubricating oil stocksuch as a distillate obtained by the vacuum distillation of crudepetroleum or by the deasphalting of a vacuum residuum. Sources oflubricating oil stocks which may be processed according to the inventionare West Texas crude, Louisiana crude, Coastal crude and the like. It isan unexpected feature of my invention that the mild hydrogenationconditions result in increased solvent refining response not only inlight clean stocks but also in relatively dirty stocks containing atleast lpercent Conradson Carbon such as deasphalted residuum. Inaddition, the combination of mild hydrogenation with N-methylpyrrolidone as the solvent results in products of good color, even whenthe stock contains more than 1 percent Conradson Carbon.

The first step in my process is a mild hydrogenation. It is to bedistinguished from the severe hydrorefining used as a substitute forsolvent extraction for the saturation of aromatics to improve the VI ofthe lubricating oil. The mild hydrogenation conditions include apressure not greater than 600 p.s.i.g, preferably 300-500 p.s.i.g.Temperatures may range from about 575 to about 800 F., preferred rangebeing 575-650 F. Hydrogen is introduced into the reaction zone at a rateof BOO-5,000 or more s.c.f.b. (standard cubic feet per barrel ofcharge), a preferred rate being from 500-2,000 s.c.f.b. Space velocities(volumes of oil per volume of catalyst per hour) may range from about0.2-3, preferably from 0.5-1.5.

The catalyst used in the mild hydrogenation step comprises ahydrogenating component advantageously carried on an inert support.Suitable hydrogenating components comprise Group VIII metals or theircompounds such as the oxides or sulfides or mixtures thereof. Examplesof Group Vlll metals are iron, nickel, cobalt, platinum and palladium.Advantageously the Group Vlll metal or compound is used in conjunctionwith the Group Vl metal such as molybdenum, tungsten or chromium orcompounds thereof. The catalyst support suitably comprises a refractoryinorganic oxide material such as silica, alumina, magnesia, titania ormixtures thereof. The support should be relatively inert and have littleif any activity at reaction conditions.

Particularly suitable catalysts are those containing from 2-8 percentcobalt or nickel and 5-20 percent molybdenum or 2-l0 percent nickel and10-30 percent tungsten by weight of the total catalyst compositesupported on alumina. Due to the mildness of the hydrogenatingconditions, the liquid yield of product is essentially l00 percent thatof the charge.

The mildly hydrogenated oil is then subjected to solvent refining with asolvent having an affinity for aromatic hydrocarbons which is at mostonly partially soluble in the oil so that two phases can be formed, anextract phase containing solvent and dissolved aromatics and a raffinatephase. Suitable solvents are furfural, nitrobenzene, dimethyl formamide,liquid S0 and the like. Solvents are generally used at dosages of -600percent, at temperatures between l20-250 F., preferred conditions beingdosages of 100-300 percent and temperatures between and l8'0 F. Aparticularly suitable solvent is N-methyl pyrrolidone which can be usedat a lower temperature and lower dosage than the other solventsmentioned above. ln addition N-methyl Z-pyrrolidone is preferred becauseof its chemical stability and its ability to produce even lightercolored refined oils. The other solvents mentioned above also have atendency to produce refined oils that are degraded and darkened incolor.

To improve the pour point of the oil the raffinate recovered from thesolvent refining is dewaxed. Dewaxing is generally effected bycontacting the raffinate from the solvent extraction with a preferentialsolvent to separate waxy from nonwaxy material. Suitable solventscomprise a mixture of an aromatic hydrocarbon such as benzene, tolueneor xylene with an alkyl ketone containing from three to eight carbonatoms such as acetone, methyl ethyl ketone, methyl propyl ketone and thelike. Depending on the desired pour point and miscibilitycharacteristics, the solvent may contain from about 40-60 percent ketoneand 60-40 percent aromatic hydrocarbon. Dilution is generally in therange of 1.5-5 parts of solvent per part of oil. The mixture is chilled,filtered and washed, the filtering temperature being selected inaccordance with the desired pour point. Generally, the filtering iscarried out at a temperature of from +20 F. to 30 F.

In the following example which is submitted for illustrative purposesonly, oil 1 is a light distillate derived from a mixed base crude, oil 2is also a light distillate derived from Louisiana crude, oil 3 isdeasphalted residuum from West Texas Crude and oil 4 is derived frommixed base crude.

In each case, the hydrogenation catalyst contains 2.3 percent Ni and10.0 percent Mo (as the oxide) supported on alumina, the solvent used inthe solvent extraction step is N- methyl 2-pyrroliclone and that used inthe dewaxing step is a mixture containing 50 percent methyl ethyl ketoneand 50 percent toluene. Data for the treatment of the various oils apinghyrogenation product to solvent extraction at a temperature betweenabout 120 and 250 F. with a solvent having an affinity for aromatichydrocarbons at a solvent to oil volume ratio of between 1:1 and 6:1 toproduce an aromatic-rich extract and an aromatic-poor raffinate, anddewaxing the raffinate using as solvent a mixture comprising an alkylketone containing from three to eight carbon atoms and an aromatichydrocarbon selected from the group consisting of benzene, toluene andxylene.

2. The process of claim 1 in which 'the hydrogenation catalyst comprisesnickel and molybdenum.

3. The process of claim 1 in which the solvent having an affinity foraromatics comprises N-methyl pryrrolidone.

pear in table 1 below. 4. The process of claim 3 in which thetemperature IS TABLE I A B A B A B A B Hydrogenating conditions:

Temperature, F :07 Pressure, p.s.i.g 500 S a velocity, v./hr./v 50 ts 2,S-c-L/bbl 1, 000 Gravity, API 23. 9 26. 2 23 4 Flash, 00C, F 460 405 490Viscosity, SUS at 210 F 66. 6 52. 115 g Viscosity index 77. 0 85. 0 0Carbon residue, percent 0 27 Refractive index at 70 C- 1. 4868 1. 4804 14920 Solvent refining:

Dosage, percent 120 110 120 Temperature, F-.. 130 130 150 Yield, volumepercent 73. 8 78. 2 7 9 Refined oil tests:

revity, API 30. 3 30. 3 1 F1851], COG, F 445 435 550 Viscosity, SUS at210 F 51. 0 60.6 90 9 Viscosity Index 105 99 95 Refractive Index 1.4633 1. 4639 4714 Solvent dewaxing:

Dilution ratio 3:1 3:1 3:1 Wash ratio 2:1 2:1 2:1 Tenapefiigurg F 0 0 0Dewexe 0 es Viscosity,IS g8 at 210 F 55. 3 55. 2 82 Viscosity 11 exP0111, +10 +5 It can be seen from the foregoing that the mildlyhydrogenated oils have higher API gravities, lower refractive indexesand higher Yl's than the charge stocks. The mildly hydrogenated oils arealso improved charge stocks for the solvent extraction resulting inyield increases of up to 10 percent when refining to the same qualitylevel. This is true even when charge stocks containing more than 1percent Conradson Carbon are used. In addition, the combination of mildhydrogenation followed by extraction using N-methyl pyrrolidone as thesolvent results in finished products of good color.

Since the hydrogenation step is carried out at such a lowpressure, myprocess has advantages over prior art processes. In a specificembodiment of my invention, a crude oil is fractionated to produce anaptha, a lubricating oil stock is recovered from the heavier thannaphtha fraction either by vacuum distillation or by deasphalting theresiduum or both, the naphtha is catalytically reformed and effluenthydrogen without repressuring or purification is used for the mildhydrogenation vof the lube oil stock. Advantageously, the reformerhydrogen can be used in the mild hydrogenation step on a once-throughbasis and returned to the reformer recycle stream.

Other modifications of the invention as hereinbefore set forth may bemade without departing from the spirit and scope, thereof, andtherefore, only such limitations should be imposed as are indicated inthe appended claims.

I claim:

1. A method for refining a lubricating oil stock which consists ofpassing said lubricating oil stock into contact with a hydrogenationcatalyst under mild hydrogenation conditions including a temperaturebetween 575 and 800 F., and a pressure between about 250 and 600p.s.i.g., to obtain a product liquid yield of substantially 100 percent,subjecting the resultbetween l20 and 180 F. 5. The process of claim 1 inwhich the dewaxing solvent comprises methyl ethyl ketone and toluene. I6. The process of claim 1 in which the hydrogenation temperature is notgreater than 650 F. and the hydrogenation pressure does not exceed 500p.s.i.g.

7. The process of claim 3 in which the lubricating oil stock contains atleast 1 percent Conradson Carbon.

8. The process of claim 3 in which the solvent to oil volume ratio isbetween l:l and 3:1.. 9. A process for the production of a lubricatingoil which comprises fractionating a crude petroleum oil to recover anaphtha fraction therefrom, recovering a lubricating oil stock from theheavier than naphtha fraction, catalytically reforming the naphthafraction, separating from the reformer effluent a hydrogen-rich stream,treating said lubricating oil stock in a process which consists ofcontacting same with a hydrogenation catalyst in the presence of atleast a portion of said hydrogen-rich stream at a temperature betweenabout 575 and 800 F. and a pressure between about 250 and 600 p.s.i.g,the pressure in the hydrogenation zone being substantlally equal to thepressure in the catalytic reforming zone, subjecting the resultinghydrogenation product to solvent extraction at a temperature betweenabout and 250 F. with a solvent having an affinity for aromatichydrocarbons at a solvent to oil volume ratio of between l:l and 6:1 toproduce an aromatic-rich extract and an aromatic-poor raffimate, and

:dewaxing the rafiinate using as solvent a mixture comprising an alkylketone containing from three to eight carbon atoms and an aromatichydrocarbon selected from the group consisting of benzene, toluene andxylene.

10. The process of claim 9 in which the hydrogen-rich stream is passedthrough the hydrogenation zone on a oncethrough basis.

2. The process of claim 1 in which the hydrogenation catalyst comprisesnickel and molybdenum.
 3. The process of claim 1 in which the solventhaving an affinity for aromatics comprises N-methyl pryrrolidone.
 4. Theprocess of claim 3 in which the temperature is between 120* and 180* F.5. The process of claim 1 in which the dewaxing solvent comprises methylethyl ketone and toluene.
 6. The process of claim 1 in which thehydrogenation temperature is not greater than 650* F. and thehydrogenation pressure does not exceed 500 p.s.i.g.
 7. The process ofclaim 3 in which the lubricating oil stock contains at least 1 percentConradson Carbon.
 8. The process of claim 3 in which the solvent to oilvolume ratio is between 1:1 and 3:1.
 9. A process for the production ofa lubricating oil which comprises fractionating a crude petroleum oil torecover a naphtha fraction therefrom, recovering a lubricating oil stockfrom the heavier than naphtha fraction, catalytically reforming thenaphtha fraction, separating from the reformer effluent a hydrogen-richstream, treating said lubricating oil stock in a process which consistsof contacting same with a hydrogenation catalyst in the presence of atleast a portion of said hydrogen-rich stream at a temperature betweenabout 575* and 800* F. and a pressure between about 250 and 600 p.s.i.g,the pressure in the hydrogenation zone being substantially equal to thepressure in the catalytic reforming zone, subjecting the resultinghydrogenation product to solvent extraction at a temperature betweenabout 120* and 250* F. with a solvent having an affinity for aromatichydrocarbons at a solvent to oil volume ratio of between 1:1 and 6:1 toproduce an aromatic-rich extract and an aromatic-poor raffinate, anddewaxing the raffinate using as solvent a mixture comprising an alkylketone containing from three to eight carbon atoms and an aromatichydrocarbon selected from the group consisting of benzene, toluene andxylene.
 10. The process of claim 9 in which the hydrogen-rich stream ispassed through the hydrogenation zone on a once-through basis.